1. Field of the Invention
The present invention relates to a system for coupling drive and driven shafts. More particularly, it relates to a coupling system which is capable of accommodating angular misalignment and axial displacement. These coupling systems are often known as flexible couplings.
2. Description of the Prior Art
Flexible couplings are designed to allow the transmission of power between a drive shaft and a driven shaft, and usually include spline teeth which are in full contact along their flanks. These couplings permit axial displacement between the shafts and allow a limited amount of angular misalignment. The amount of misalignment depends upon the tooth shape and the amount of play between teeth and the drive and driven numbers. Metallic splines cannot accept relatively high amounts of misalignment, since the loss of contact area from misalignment results in high tooth stresses and fretting.
Non-metallic splines interpose a plastic bushing between mating teeth of the drive and driven shafts. This plastic bushing virtually eliminates the fretting problem described above with metallic splines. Only the expendable, inexpensive bushing is subject to wear. Attempts have been made to apply non-metallic spline couplings in situations where it is difficult to control the amount of angular misalignment. Such applications include aircraft and helicopter accessory drives, which are subject to changing angular misalignment, changing speeds and changing torques. As an example, in helicopter rotor drives, misalignments of as much as five degrees are encountered. Prior attempts to solve these problems have not satisfactorily provided increased clearance at the ends of the spline teeth for accommodating misalignment while simultaneously maintaining a relatively constant bearing surface area. Previous couplings have allowed only very minor amounts of misalignment.